VT100 terminfo problem

[Doug Gwyn]

In article <68816 at sun.uucp> guy at gorodish.Sun.COM (Guy Harris) writes:
>The *ONLY* time "raw" mode should be used for "full-screen" interactive
>applications are those times when:

Add another one:
	5) keys must not generate signals.

As I'm sure Guy knows, 7th Edition-based tty handler modes were just
not sufficiently fine-grained and orthogonal.  The USG tty handler
was a considerable improvement in this regard, and any POSIX-conforming
implementation will be.

>If it spent enough time at that level, and if the serial port was run at a
>high-enough baud rate, it is conceivable that the driver might not see the
>interrupt indicating that the ^S came in, and thus might not see the ^S itself,
>in time to stop output before the VT100's buffer overran.

This problem can really occur only if the tty port output is done
in large chunks, for example via DMA, and no provision has been made
for incoming tty port input to be immediately processed and the DMA
aborted when a DC3 is seen.  I've seen a botch like this, by the way,
but since the vendor fixed their hardware, firmware, and software to
solve the problem I don't think I need to say who it was.